Driving device

ABSTRACT

The driving device comprises a hydraulically shiftable friction coupling and a friction brake by means of which an input can be connected to a gear and which perform the function of a parking brake wherein an auxiliary release device comprising an adjustable accumulator piston and gear shift pistons interacting therewith separate friction coupling and friction brake thus interrupting the drive train; the accumulator cylinder of the auxiliary release device is connected to a supply tank via a connecting line and is provide with a blocking device which cuts off the connection to the supply tank when the auxiliary release device is actuated.

FIELD OF THE INVENTION

This invention relates to a driving device, particularly for driving thewheels of a motor vehicle such as excavators and wheel loaders.

BACKGROUND OF THE INVENTION

In power shift transmissions, such as used in industrial vehicles, it isknown to provide an auxiliary release device by which the drive train ofthe vehicle is interrupted thus making it possible to tow a vehicle thathas broken down.

The Applicant's DE 44 08 472 describes a driving device which isprovided with an input, a mechanical gear rear-mounted thereon and twohydraulically shiftable friction couplings and friction brakes throughwhich the input can be connected with the gear and which perform thefunctions of a parking brake. Friction coupling and friction brake areconnected via control-pressure lines with an auxiliary release devicewhich has an adjustable accumulator piston and gear shift pistonsinteracting therewith so that when the accumulator piston is actuated,the gear shift pistons supply the contents of the accumulator piston viathe control-pressure lines of the friction coupling and of the frictionbrake in the sense of a separation.

The device can have a compensation cylinder where is situated acompensation piston prestressed by a spring device and connected withthe contents of the accumulator piston so that in the hydraulic systemof the auxiliary release device an even pressure always prevails andpressure changes due to temperature oscillations are compensated withoutproblem.

SUMMARY OF THE INVENTION

The problem on which this invention is based is further to simplify theconstruction of such a driving device with which a vehicle in brokendown state can be towed without problem and thereby to reduce the costof production.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in detail below with reference to the drawingin which an advantageous embodiment is shown.

In the only FIGURE is diagrammatically shown in unactuated state theessential part of the driving device together with the auxiliary releasedevice.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A driving train designated with 1 having an input 1A and an output 1B isseparated in a manner known per se with a hydraulically actuatedcoupling device 2 which has a friction coupling 3 and a friction brake4, wherein the latter does not perform the actual function of a brakebut constitutes a coupling in which the outer discs are firmly situatedwithin the coupling housing. In the friction coupling 3 both the innerand the outer discs can rotate.

For supply of the device with hydraulic oil, a pump 5 is providedwherein the coupling and uncoupling of the coupling device 2 iscontrolled by a magnetic valve 6.

The magnetic valve 6 is here shifted in a manner such that in case offailure of the pump 5 or generally in case of pressure drop within thehydraulic system, the coupling is automatically engaged so that it isnot possible to tow the vehicle; to this end a separation of the drivetrain is necessary.

The drive train is separated by actuating an accumulator piston 7 in anaccumulator cylinder 8. The accumulator piston 7 is actuated manually,e.g. with an appropriately profiled part upon the accumulator piston 7in the form of a hexagon or inner hexagon upon which a suitable tool isfastened in order to move the accumulator piston 7 by hand.

In the embodiment shown, the accumulator piston 7, which is moved intothe accumulator cylinder 8, has an accumulator piston projection 31which is provided with an outer thread and which extends into aconnecting line segment 9 which extends from accumulator cylinder 8 to aconnecting line 21 which extends to an oil supply tank 22. Theaccumulator piston projection 31 of the accumulator piston 7 has a hole32 extending in axial direction which, on one side, is connected withthe contents 10 of the accumulator cylinder 8 and, on the other, via aduct 33, with a reduced cross section segment 34 of the accumulatorpiston projection 31 so that in the unactuated state shown in the singlefigure there is a fluid connection of the contents 10 of the accumulatorcylinder 8 to the supply tank 22. The connecting line segment 9 isconnected to the actual connecting line 21 via a narrow point 24, saidnarrow point 24 being dimensioned so that upon actuation of theauxiliary release device, i.e. when the accumulator piston 7 moves, itsconnecting line segment 9 sealingly traverses the narrow point 24 andinterrupts the fluid connection between the contents 10 and the supplytank 22. With 35 is designated a spring-loaded recoil valve provided inthe piston projection 31 of the accumulator piston 7 and serving asoverpressure valve preventing an inadmissibly high pressure in thesystem when the auxiliary release device is actuated.

In a normal driving state, the contents 10 of the accumulator cylinder 8is connected with the supply tank 22 so that the oil chamber can becompletely filled after actuation of the auxiliary release device;during actuation of the auxiliary release device the connection betweensupply tank 22 and contents 10 is cut off.

When the accumulator piston 7 moves, the oil located in the contents 10is, in a conventional manner, fed via the auxiliary device control lines11, 12 to the two gear shift valves 13, 14 so that the gear shiftpistons 15, 16 placed therein are actuated and moved against the forceof a spring device 17, 18 to the extent that the openings of the brakeand clutch actuating lines 19, 20 branching off from the gear shiftvalves 13, 14 become released.

A direct hydraulic connection thus exists via the brake and clutchactuating lines 19, 20 between the contents 10 of the accumulatorcylinder 8 and the coupling device 2 so that, e.g. the friction coupling3 can be disengaged by the gear shift element 13 and the friction brake4 by the gear shift valve 14. The disengagement results against theresistance of pressure springs 29, 30 in the coupling device 2.

In order that as result of too great a reduction of the contents 10 ofthe accumulator cylinder 8, i.e. of too large an amount of oil beingremoved for the contents 10, there will not generate within thehydraulic circuit a pressure too elevated, the overpressure valve 35 isprovided at the end of the hole 32 in the projection 31 of theaccumulator piston 7. Thereby care is also taken that duringoscillations of the oil temperature the amount of oil located in theclose circuit be constant so that no erroneous actuation of the gearshift pistons 15, 16 can occur.

Seals 25, 26 provided in the gear shift valves 13, 14 prevent that oilfrom the closed circuit from penetrating the gear shift control-pressurelines 27, 28. The seal 36 prevents oil from escaping from the contentsof the cylinder 10.

If the normal driving operation should be resumed, the separation of thedrive train 1 has to be canceled again. To this end, the accumulatorpiston 7 is manually moved to its initial position, e.g. by contraryrotation of the inner hexagon whereby the projection 9 can be guidedinto a thread. Thereby the contents 10 in the accumulator cylinder 8again increase due to the receding oil whereby the friction coupling 3and the friction brake 4 are again engaged. The prestressed pressuresprings 29, 30 in the coupling device 2, which always produce anautomatic engagement of the coupling device 2, in case the oil pressurewithin the closed hydraulic circuit should drop, produce the engagement.

The prestressed pressure springs 17, 18 in the gear shift valves 13, 14now move the gear shift pistons 15, 16 likewise again to their initialposition so that the oil contents existing in the gear shift valves 13,14 again flow into the accumulator cylinder 8.

Since, as already said, upon an actuator of the auxiliary release deviceboth the friction coupling 3 and the friction brake 4 are disengaged,even in case of an unintended actuation of the input no power istransmitted so that the vehicle cannot be unintentionally moved.

Reference numerals

1 drive train

2 coupling device

3 friction coupling

4 friction brake

5 pump

6 magnetic valve

7 accumulator piston

8 accumulator cylinder

9 connecting line segment

10 contents of the cylinder

11 auxiliary device control line

12 auxiliary device control line

13 gear shift valve

14 gear shift valve

15 gear shift piston

16 gear shift piston

17 pressure spring

18 pressure spring

19 brake actuating line

20 clutch actuating line

21 connecting line

22 supply tank

23 seal

24 narrow point

25 seal

26 seal

27 gear shift control-pressure line

28 gear shift control-pressure line

29 pressure spring

30 pressure spring

31 accumulator piston projection

32 hole

33 duct

34 reduced cross section segment

35 overpressure valve

36 seal

What is claimed is:
 1. A driving device, for driving the wheels of a motor vehicle, an input, an output and two shiftable friction couplings (3, 4) wherein: said friction couplings (3, 4) are closed by spring tension to connect the input to the output and opened by hydraulic pressure supplied to said friction couplings (3, 4) via gear shift valves (13, 14) and appertaining brake and clutch control-pressure lines (19, 20) to disconnect the output from the input; both friction couplings (3, 4) are closed by said spring tension when the pressure drops in the hydraulic system and perform the function of a parking brake, gear shift pistons (15, 16) of said gear shift valves (13, 14) interactingly connected via auxiliary device control lines (11, 12) with an auxiliary release device which has an adjustable accumulator piston (7) and an accumulator cylinder (8) and which, in an unactuated state, contains a pressureless oil content; and upon actuation of said accumulator piston (7), oil contents accumulated in said accumulator cylinder (8) displaces said gear shift pistons (15, 16) in order to connect said auxiliary device control lines (11, 12) with said brake and clutch control-pressure lines (19, 20) so that the oil contents accumulated in said auxiliary release device opens said friction couplings; said accumulator cylinder (8) is connected via a connecting line (21) with a supply tank (22), and said accumulator piston (7) of said auxiliary release device including an accumulator piston projection (31) extending into a connecting line segment (9) of said connecting line (21), and said connecting line (21) includes a narrow point 24 between said connecting line segment (9) and said connecting line (21) and on the transition of said accumulator piston projection (31) to said connecting line (21) which upon actuation of said accumulator piston (7) is traversed in tight manner by a reduced cross section segment (34) of said accumulator piston projection (9) of said accumulator piston (7) to interrupt the connection to said supply tank (22) upon actuation of said accumulator piston (7) of said auxiliary device.
 2. The driving device according to claim 1, wherein said accumulator piston projection (31) of said accumulator piston (7) is traversed by an axial hole (32) which is connected on one side with the contents (10) of said accumulator cylinder (8) and on the other, via a duct (33), with the outer wall of said reduced cross section segment (34) of said accumulator piston projection (31) so that in unactuated state of said auxiliary release device a fluid connection exists between contents (10) and supply tank (22).
 3. The driving device according to claim 1, wherein an end of said hole (32) facing said narrow point (24) is provided in said accumulator piston projection (31) with a spring-loaded overpressure valve (35).
 4. The driving device according to claim 1, wherein said accumulator piston (7) is manually actuatable.
 5. The driving device according to claim 4, wherein said accumulator piston (7) is axially movable via a thread placed on said accumulator piston projection (31).
 6. The driving device according to claim 5, wherein said accumulator piston (7) is provided with a hexagonal head or with an inner hexagon.
 7. The driving device according to claim 1, wherein said gear shift pistons (15, 16) are provided with spring devices (17, 18) which press said gear shift pistons back to initial or basic position.
 8. The driving device according to claim 1, wherein said auxiliary release device is integrated in the gear block of the motor vehicle.
 9. The driving device according to claim 1, wherein the oil contents of said auxiliary release devices are separated by seals (25, 26) from said gear shift control-pressure lines (27, 28) of said gear shift pistons (15, 16).
 10. The driving device according to claim 9, wherein said seals (25, 26) are provided upon said gear shift pistons (15, 16). 